Multiple-wavelength physiological monitor

A physiological monitor for determining blood oxygen saturation of a patient, the physiological monitor comprising:

• a pulse oximetry sensor, wherein the pulse oximetry sensor comprises:
• three or more light emitting diodes, wherein each light emitting diode is operative to emit light of a different wavelength;
• and
• a detector adapted to receive light from the three or more light emitting diodes after being attenuated by tissue of a medical patient, wherein the detector provides an output signal based at least in part upon the received light;
• and
• a processor configured to:
• compute a ratio based at least in part on three or more plethysmographic signals obtained from the output signal, the ratio comprising a quotient of a first weighted sum of the plethysmographic signals multiplied by a first set of vector coefficients and a second weighted sum of the plethysmographic signals multiplied by a second set of vector coefficients, the first and second sets of vector coefficients determined based upon calibration data or fitting of experimental data;
• and
• determine the blood oxygen saturation of said medical patient based at least in part upon a single blood oxygen saturation curve using said ratio, wherein said blood oxygen saturation of said medical patient determined based at least in part on the blood oxygen saturation curve is configured to exhibit higher accuracy at lower perfusion levels compared to a two wavelength blood oxygen saturation system;
• output the oxygen saturation for display to a clinician;
• wherein the processor compensates the blood oxygen saturation of said medical patient with data regarding blood constituents other than the blood oxygen saturation, wherein said blood constituents comprise methemoglobin, carboxyhemoglobin, and hemoglobin in said medical patient's blood.